Overlapping-rod type vacuum circuit interrupter

ABSTRACT

A vacuum circuit interrupter of the overlapping-rod type comprises two spaced-apart conductive rods having longitudinally overlapping portions that are disposed in side-by-side laterally spaced relationship. Each one of a pair of bridging contacts engages the sides of the overlapping rod portions at spaced points on the bridging contact and serves to carry current between the rods when the interrupter is closed. The two bridging contacts are located closely adjacent each other on opposite sides of the two rods and are movable during interrupter-opening away from each other and away from the two rods.

United States atent 1191 Win11 3,839,611 Oct. 1, 1974 UVERLAIPIPING-ROD TYPE VA C UUM ClltClUllT llN'lllERlUlP'lllER Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-William Freedman; J.

[75] Inventor: Ulrver 1H1. Winn, Marlton, NJ. Wesley Haubner [73] Assignee: General Electric Company,

Philadelphia, Pa. [22] Filed: Aug. 27, 11973 [57] ABSTRACT [21] Appl' 391558 A vacuum circuit interrupter of the overlapping-rod type comprises two spaced-apart conductive rods hav- [52] US. Cl. 2011/1144 B ng l ngi in lly o rl pping portion that are dis- [51] Int. Cl. H0111 33/66 posed yd lat rally spaced relationship. [58] Field of Search 200/144 B a one of a pair of bridging conta ts engages the sides of the overlapping rod portions at spaced points [56] Referen es {Cit d on the bridging contact and serves to carry current be- UNITED STATES PATENTS tween the IOdS when the interrupter is closed. The tWO bridging contacts are located closely adjacent each 3 other on opposite sides of the two rods and are mov- 3509404 4 1970 Richmm: 3:11:31: 33:. 200 144 B able during interrupteropening away from each other 3,575,564 4/1971 Weston 200/144 B and away from the two rods- FOREIGN PATENTS OR APPLICATIONS 9 Claims, 4 Drawing Figures 1,269,421 7/1961 France ZOO/144 B 2 0 lAX\ \k \\\\\W Zl E 30" l l 36 f a? j??? "70 l r T 3 2 1 fig A5- 1 Q 1 d7- 24% 1 1 1st t \\\\\\Q BACKGROUND This invention relates to an electric circuit interrupter of the vacuum-type and, more particularly, to a vacuum-type circuit interrupter that comprises overlapping-rod electrodes between which high-current arcs can burn in a diffuse manner without forming destructive anode spots.

Vacuum interrupters of this general type are shown in US. Pat. No. 3,321,598-Streater, 3,471,734-Rich, and 3,679,474Rich. Also of inter est are US. Pat. No. 3,356,893-Lafferty; 3,471,733Rich; 3,643,047--'Rich; 3,l85,798-Titus; 3,575,564-Weston; and German Democratic Republic Pat. No. 88,585.

According to US. Pat. No. 3,47l,734-Rich, the arc in an overlapping-rodelectrode type of vacuum interrupter is able to remain diffuse and to carry high currents without forming destructive anode spots because in such an interrupter the body force F that acts on the conduction paths through the arc discharge is limited to a very low level. The tendency to cause the conduction paths between a pair of opposite polarity arc electrodes to bunch together and develop a high current density which results in formation of an anode spot appears to be directly related to the body force F. By

keeping F low, this tendency to bunch is kept correspondingly low.

Still another object is to provide contact structure for an overlapping-rod type vacuuminterrupter which, as compared to conventional contact structures for such interrupters, is able to utilize reduced forces for holding the contacts in high-pressure engagement during high momentary currents through the contacts.

Still another object is to provide insulated contact structure for an overlapping-rod type vacuum interrupter which, as compared to conventional contact structure for such interrupters, provides improved capabilit'y of withstanding recovery voltage and other voltages applied across the interrupter.

In carrying out the invention in one form, I provide a vacuum interrupter that comprises two spaced-apart conductive rods having longitudinally overlapping portions that are disposed in side-by-side laterally spaced relationship. The interrupter also comprises two bridging contacts, each engaging the sides of the overlapping rod portions at spaced points on the bridging contact and thus serving to carry current between the rods when the interrupter is closed. The two bridging contacts are located closely adjacent each other on opposite sides of the two rods so that when the interrupter is closed, current through the bridging contacts develops a magnetic effect urging the bridging contacts toward each other and into firmer engagement with the sides of the rods. The bridging contacts are moved during an interrupter-opening operation away from each The body force F can be kept low byseverely limiting the density B of the magnetic field component that extends transversely of the conduction paths through the arc discharge. This follows because the body force F is determined by:

where J is the current density and B is the flux density of the transverse magnetic field component.

In the overlapping-rod type interrupter, the transverse magnetic field component B and the resulting body force F are low only when the arc is positioned between the overlapping rods. It would therefore be ideal to initiate the arc between the rods and to maintain it in this position at all times. This idea], however, is difficult to achieve in a practical design of interrupter that normally carries current through a set of contacts within the interrupter. In such an interrupter, the contacts are usually spaced by a substantial distance from the gap between the rods, and the arc initiated between the contacts at the instant they separate must be transferred across this substantial distance from its initiation region into the gap between the rods. Such transfer is not always as rapid as might be desired.

SUMMARY vacuum interrupter-in which the total mass of the mov-- able contact structure is low compared to conventional contact structures for such interrupters.

- tionship,

other and away from the two rods.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a vacuumtype circuit interrupter comprising a highly evacuated envelope l0, pressure within which is normally at a level of 10 torr or lower. The envelope 10 comprises a tubular casing comprising two tubular members 12 of insulating material and a cylindrical midsection 14 of metal joined at its opposite ends to the tubular members 12 by suitable glass-to-metal seals 15. At opposite ends of this tubular casing 12, 14, there are two metal end caps 20 and 21 which are joined to the casing by means-of suitable vacuum-tight seals 24. These end caps act as opposed electrical terminals for the interrupter.

Electrically connected to the end caps 20 and 21 are two rod electrodes 26 and28. These rod electrodes 26 and 28 extend longitudinally of the casing l2, l4 and are disposed in generally parallel, spaced-apart relaoverlapping longitudinally. Each of these electrodes is preferably of a composite structure, comprising an inner core 30 of a high strength steel and an outer core 32 of a suitable copper alloy or the like for imparting high conductivity to the electrode structure.

For carrying current between the rod electrodes 26, 28, a pair of bridging contacts 34 and 35 are provided. When the interrupter is in its closed position of FIGS. 1 and 2, these bridging contacts engage the sides of the rod electrodes at a location where the electrodes overlap, thus providing an electrical path between the electrodes. Opening of the interrupter is effected by substantially simultaneously driving the bridging contacts radially outward away from each other and away from the rod electrodes. For driving the bridging contacts radially outward, operating rods 36 and 37 are provided. Operating rod 36 is pivotally connected to bridging contact 34, and operating rod 37 is pivotally connected to the other bridging contact 35. These operating rods 36 and 37 are coupled together by a suitable linkage (not shown) external to the envolope 10, which forces any movement of the rods to be in opposite directions and substantially equal. For providing a seal that permits each contact to be moved radially in the above-described manner without impairing the vacuum inside the envelope, a flexible metal bellows 39is pro vided for each contact. This bellows has one end suitably joined in sealed relationship to the midsection 14 of the envelope l and its other end suitably joined in sealed relationship to a radially outwardly projecting portion 41 of the bridging contact.

To allow each bridging contact to firmly engage both rod electrodes 26 and 28 without interference from either rod electrode despite uneven wear of the rod electrodes or contacts, a pivotal joint 40 is provided between each bridging contact and its associated operating rod. This pivotal joint 40 is disposed outside the evacuated envelope and thus may 'be suitably lubricated and is not subject to the galling action typically produced by frictional contact in a vacuum environment. A cup-shaped shield 43 is disposed around the inner end of the bellows 39 to protect it against hot arcing products generated at the contacts during an interrupting operation.

When the bridging contacts are separated from the rod electrodes 26 and 28 during an interrupting operation, a pair of series-related arcs are formed, one between rod 26 and one of the bridging contacts and the other between rod 28 and one of the bridging'contacts. FIG. 3 shows two such arcs at 50 and 52. Each of these arcs is established in a region where the magnetic field that extends transversely of the arc has a high density. This will be apparent from FIG. 3 where typical lines of flux resulting from current through the rods are illustrated at 54 and 55 extending transversely of the arcs 50 and 52. This high density transverse magnetic field tends to cause any are therein to develop a relatively high arc voltage. In the gap region 58 between the two rods, the flux from the current through the two rods largely cancels each other, thus providing a region of low density transverse magnetic field where an are extending between the two rods can burn with a low arc voltage. An arc has a strong tendency to move into the.

region where it can burn with least arc voltage, and thus each of the arcs moves quickly from its illustrated position into the gap region 58 between the rods. The close proximity of the arc-initiation regions to the gap region 58 also contributes to the rapidity with which the arc is transferred into the gap region 58.

In the low magnetic field region 58 between the rods, the arc can burn in a diffuse manner without forming destructive anode spots even at high currents, as has been pointed out by J. A. Rich in his aforesaid U.S. Pat. No. 3,471,734. An arc in this diffuse state will produce little arc-erosion of the parts and a substantially reduced volume of arcing products as compared to the are that burns with an anode spot. Thus, the above described rapid transfer of the arcs into this region of low transverse magnetic field reduces erosion of the parts exposed to the arc and also reduces the volume of arc-.

ing products generated, thus facilitating interruption.

An additional factor contributing to rapid arc transfer is that the arc voltage of only a single arc is developed by current passing directly between the rods as compared to the arc voltages of two arcs in series when arcs 50 and 52 are present at the start of an interrupting operation. The resulting higher impedance in the path through the partially open bridging contact tends to divert current into the lower impedance arcing path directly between the rods.

For condensing the arcing products that are generated during an interrupting operation, a tubular metal shield 51 is provided. This shield is spaced from the rods and is electrically isolated from both terminals 20 and 21 of the interrupter. It is preferably at a substantially mid-potential with respect to these terminals. In one embodiment of the invention, the shield 51 is supported on metal midsection 14 of the envelope 10 by suitable conductive means 53 (FIG. 2) which also electrically interconnects the shield and the midsection. Since the bridging contacts 35 are also connected to the midsection 14, it will be apparent that the bridging contacts 35, the shield 51, and the midsection 14 are all at the same potential.

As will be apparent from FIGS. 2 and 4, the tubular metal shield 51 has circumferentially spaced openings 56 through which the bridging contact structures are freely movable in a radial direction. During the final stages of an opening operation, the bridging contacts recede partially through these openings into their positions shown in FIG. 4. In these positions, the bridging contact structures are in regions of relatively low intensity electric field. This substantially reduces the likelihood of electrical breakdowns between the rods and the bridging contact, as does the fact that the bridging contacts are protected from severe pitting and arcerosiofi by the above described rapid transfer of the arc into the inter-rod gap region 58.

In another embodiment of my invention (not shown), the movable bridging contacts 34, in opening, are withdrawn even further than illustrated in FIG. 4 into positions located radially outside the shield openings 56. This further reduces the intensity of the electric field adjacent the open bridging contacts, thus further reducing the likelihood of electrical breakdowns between the rods and the bridging contacts.

Closing of the interrupter is effected by returning the bridging contacts from their open positions of FIG. 4 to their closed positions of FIGS. 1 and 2. Near the very end of the closing stroke, it is possible for a prestrike to occur between one of the rods and one of the approaching bridging contacts. However, the fact that there are two gaps in series between each bridging contact and the two rods delays the occurrence of any such prestrike and reduces the likelihood that it will be a problem.

The higher dielectric strength resulting from the presence of two gaps in series between each bridging contact and the two rods 26, 28 is also advantageous during an opening operation in that it reduces the likelihood of an arc-restrike or reignition through the bridging contact should a current zero occur at an instant when the bridging contact has been only partially withdrawn to its fully open position.

Another advantage of using bridging contacts is that the mass of the moving contact structure can be substantially reduced as compared to the usual contact arrangement such as shown in U.S. Pat. No. 2,949,520--Schneider, assigned to the assignee of the present invention, where one of the massive conductive rods forms a part of the movable contact structure. in a bridging contact arrangement, the only currentconducting part requiring movement is the bridging contact itself, or, in the illustrated embodiment, the two bridging contacts. This low contact mass enables me to effect very high speed contact motion, thus contributing to more rapid arc transfer into the inter-rod gap 58 and also contributing to more precise control of the contact opening operation. With respect to the latter point, the low-mass bridging contact structure lends itself especially well to use in a synchronous opening arrangement, such as described in U.S. Pat. No. 3,555,354Kotos, assigned to the assignee of the present invention.

Another advantage of my bridging contact structure is that reduced forces can be relied upon to hold the contacts in engagement against high momentary cur rents. Referring to FIG. 2, since current flows through the bridging contacts in the same direction, there is an attractive magnetic force between the two bridgingcontacts varying directly with the current square tending to force the bridging contacts into firmer engagement with the rods.

it will be noted that in the illustrated embodiment the closing forces applied to the rods act in opposite directions on the rods and thus tend to balance each other. in a preferred form of the invention, these forces are of substantially equal magnitude. As a result, when both bridging contacts are in their closed positions, closing forces on them are substantially cancelling out each other and applying no substantial net force to the rods tending to bend them.

in another embodiment of the invention, the bridging contacts 34, 35, when open, are electrically isolated from the metal shield 51 as well as from the contact rods 16, 28. In one form of interrupter, such isolation is effected by making the supports 53 for the shield of an electrical insulating material instead of a conductive material as described hereinabove. This electrical isolation of the bridging contacts from the shield and the rods appears to improve the ability of the interrupter to withstand recovery voltage and other voltages applied across the open interrupter.

Although i prefer to utilize two bridging contacts as shown, my invention in its broader aspects also comprehends the use of a single bridging contact. Although not all of the advantages referred to hereinabove are realized with such an interrupter, some of them are still realized, such as the rapid arc transfer into the interrod gap 58, the reduced contact mass, and the two gaps in series features.

While 1 have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my inventron.

What I claim as new and desire to secure by Letters Patent is:

l. A vacuum-type circuit interrupter comprising:

a. a highly evacuated envelope,

b. spaced-apart terminals at opposite ends of said envelope between which a high voltage can be applied when the interrupter is open,

c. a pair of spaced-apart rods disposed within said envelope and respectively electrically connected to said terminals, said rods having longitudinally overlapping portions that are disposed in side-by-side, laterally-spaced relationship,

d. a pair of bridging contacts, each adapted when the interrupter is closed to engage the sides of the overlapping portions of the two rods at spaced points on the bridging contact and to carry current between saidrods,

e. said two bridging contacts being located closely adjacent each other on opposite sides of said pair of rods so that when the interrupter is closed, current through the bridging contacts develops a magnetic effect urging the bridging contacts toward each other and into firmer engagement with the sides of said rods,

f. said bridging contacts being movable during interrupter-opening away from each other and away from said pair of rods.

2. The vacuum type circuit interrupter of claim ii in which each of said bridging contacts extends transversely of said rods.

3. The vacuum type circuit interrupter of claim l in which:

a. arcs are initiatedin arc-initiation regions between said rods and said bridging contacts when the bridging contacts are moved out of engagement with said rods during an interrupter-opening operation,

b. the magnetic field in the gap region between said rods located adjacent said arc-initiation regions has a relatively low density in a direction transverse to a path extending directly between said rods, and

c. the magnetic field in the arc-initiation regions where said arcs are initiated has a relatively high density extending transversely of the arcs therein, thus tending to force the arcs from the arcinitiation regions into the gap region between the rods.

4. The vacuum type circuit interrupter of claim 11 in i which said bridging contacts during an opening operation move transversely of a path extending directly be tween said rods across the gap between said rods.

d. A vacuum type circuit interrupter comprising:

a. a highly evacuated envelope,

b. spaced apart terminals at opposite ends of said envelope between which a high voltage can be applied when the interrupter is opened,

c. a pairv of spaced apart rods disposed within said envelope and respectively electrically connected to said terminals, said rods having longitudinally over- 7 lapping portions that are disposed in side-by-side laterally spaced relationship,

d. a bridging contact extending transversely of said rods and adapted when the interrupter is closed to engage the sides of the overlapping portions of the two rods and to carry current between said rods,

e. said bridging contact being movable during an interrupting operation transversely of said rods.

6. An interrupter as defined in claim 1 which further comprises a tubular metal shield surrounding the region where said bridging contacts engage said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically connected to said bridging contacts and having radially extending openings therein into which the bridging contacts are retractable during an interrupting operation.

7. An interrupter as defined in claim 5 whichfurther comprises a tubular metal shield surrounding the region where said bridging contact engages said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically connected to said bridging contact and having a radially-extending opening therein into which the bridging contact is retractable during an interrupting operation.

8. An interrupter as defined in claim 1 which further comprises a tubular metal shield surrounding the region where said bridging contacts engage said rods, said shieldbeing spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically isolated from said bridging contacts when said interrupter is open and having radially extending openings therein into which the bridging contacts are retractable during an interrupting operation.

9. An interrupter as defined in claim 5 which further comprises a tubular metal shield surrounding the region where said bridging contact engages said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically isolated from said bridging contact when said interrupter is open and having a radially extending opening therein into which the bridging contact is retractable during an interrupting operation. 

1. A vacuum-type circuit interrupter comprising: a. a highly evacuated envelope, b. spaced-apart terminals at opposite ends of said envelope between which a high voltage can be applied when the interrupter is open, c. a pair of spaced-apart rods disposed within said envelope and respectively electrically connected to said terminals, said rods having longitudinally overlapping portions that are disposed in side-by-side, laterally-spaced relationship, d. a pair of bridging contacts, each adapted when the interrupter is closed to engage the sides of the overlapping portions of the two rods at spaced points on the bridging contact and to carry current between said rods, e. said two bridging contacts being located closely adjacent each other on opposite sides of said pair of rods so that when the interrupter is closed, current through the bridging contacts develops a magnetic effect urging the bridging contacts toward each other and into firmer engagement with the sides of said rods, f. said bridging contacts being movable during interrupteropening away from each other and away from said pair of rods.
 2. The vacuum type circuit interrupter of claim 1 in which each of said bridging contacts extends transversely of said rods.
 3. The vacuum type circuit interrupter of claim 1 in which: a. arcs are initiated in arc-initiation regions between said rods and said bridging contacts when the bridging contacts are moved out of engagement with said rods durinG an interrupter-opening operation, b. the magnetic field in the gap region between said rods located adjacent said arc-initiation regions has a relatively low density in a direction transverse to a path extending directly between said rods, and c. the magnetic field in the arc-initiation regions where said arcs are initiated has a relatively high density extending transversely of the arcs therein, thus tending to force the arcs from the arc-initiation regions into the gap region between the rods.
 4. The vacuum type circuit interrupter of claim 1 in which said bridging contacts during an opening operation move transversely of a path extending directly between said rods across the gap between said rods.
 5. A vacuum type circuit interrupter comprising: a. a highly evacuated envelope, b. spaced apart terminals at opposite ends of said envelope between which a high voltage can be applied when the interrupter is opened, c. a pair of spaced apart rods disposed within said envelope and respectively electrically connected to said terminals, said rods having longitudinally overlapping portions that are disposed in side-by-side laterally spaced relationship, d. a bridging contact extending transversely of said rods and adapted when the interrupter is closed to engage the sides of the overlapping portions of the two rods and to carry current between said rods, e. said bridging contact being movable during an interrupting operation transversely of said rods.
 6. An interrupter as defined in claim 1 which further comprises a tubular metal shield surrounding the region where said bridging contacts engage said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically connected to said bridging contacts and having radially extending openings therein into which the bridging contacts are retractable during an interrupting operation.
 7. An interrupter as defined in claim 5 which further comprises a tubular metal shield surrounding the region where said bridging contact engages said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically connected to said bridging contact and having a radially-extending opening therein into which the bridging contact is retractable during an interrupting operation.
 8. An interrupter as defined in claim 1 which further comprises a tubular metal shield surrounding the region where said bridging contacts engage said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically isolated from said bridging contacts when said interrupter is open and having radially extending openings therein into which the bridging contacts are retractable during an interrupting operation.
 9. An interrupter as defined in claim 5 which further comprises a tubular metal shield surrounding the region where said bridging contact engages said rods, said shield being spaced from said rods and being electrically isolated from said rods when said interrupter is open, said shield being electrically isolated from said bridging contact when said interrupter is open and having a radially extending opening therein into which the bridging contact is retractable during an interrupting operation. 